A kind of method that improves the thick and large section strand from feeding capacity
Technical field
The present invention relates to strands such as metal die casting Wide and Thick Slab base, thick and large section continuous cast round billets, square billet and rectangular bloom and make the field, specifically a kind of raising thick and large section strand is from feeding capacity, improves and eliminates the loose method with face crack of strand internal shrinkage.
Background technology
Wide and Thick Slab is widely used in China's economic construction.On large ship, ocean platform, Hydropower Unit, fired power generating unit, pressure vessel, mould manufacturing and long-distance pipeline, all use Wide and Thick Slab in a large number.China is newly-built tens of Wide and Thick Slab steel rolling production-lines in the recent period, comprise Anshan iron and steel plant 5000mm, 5500mm milling train, Baosteel 5000mm milling train etc., more than 2,000 ten thousand tons of newly-increased production capacities.Therefore, it is huge to be used for the generous slab demand of thick and large section of rolling Wide and Thick Slab.At present, the continuous casting steel billet maximum ga(u)ge is all less than 400mm, and adopting the continuous casting steel billet rolling thickness is the Wide and Thick Slab of 200mm, owing to depress than little, is difficult to guarantee the core performance.And adopt die casting method or electroslag remelting method to produce generous slab, and its production efficiency is low, and lumber recovery is low, and cost is high.Therefore, press for exploitation thickness greater than the generous slab manufacturing technology of low cost, the high efficiency of 600mm.The generous slab manufacturing of water cooled mo(u)ld is a quick technology, but when adopting the water cooled mo(u)ld method to produce generous slab, because water-cooled intensity is bigger, causes generous slab center and surface temperature difference big easily, and thermal stress is big in the process of setting, and steel slab surface and core crack.
Big section continuous cast round billets is used to replace general static ingot, and its production efficiency is high, and stock utilization is high, shows good growth momentum.Big section continuous cast round billets can be used for producing nuclear power tube class part, and wind-powered electricity generation circular piece and automobile, steamer, machinery are used crucial axial workpiece, and the target product annual production of thick and large section circle base is above 3,000 ten thousand tons.In recent years, adopting continuous casting technology to produce thick and large section circle base more and more comes into one's own.This technology be with continuous metal liquid casting in water mold, molten steel solidifies in water mold, and constantly will solidify part through the dummy ingot device and pulled out by the lower end, realizes the continuous casting of strand.Adopt this explained hereafter strand, its ratio of height to diameter is big, is difficult to realize the axis feeding of strand, causes the steel ingot central pipe with loose easily; And because the steel ingot outer surface adopts Constraint Cooling Technology, cause hull-skin temperature low excessively more, crack.These drawbacks limit the development of continuous cast round billets to bigger cross dimensions (>=Φ 800mm).
Gross imperfections such as thickness to be the above thick and large section continuous casting square billet of 400mm with rectangular bloom exist the equally loose and face crack of internal shrinkage.
Generally speaking, solve strand internal shrinkage rarefaction defect, adopt increases the rising head size or adopts insulation (heating) rising head more, realizes the consecutive solidification of strand along gravity direction.Yet the rising head ratio of thick and large section continuous casting billet is very little, and ratio of height to diameter can't be realized the axial gravity feeding of strand greater than 4.
In sum, thick and large section strand internal shrinkage loosens, face crack is the technical bottleneck of restriction strand to bigger cross dimensions development.Therefore, improve the feeding capacity in the thick and large section casting blank solidification process, it is loose most important with surface crack defect to solve thick and large section strand internal shrinkage.
Summary of the invention
The object of the present invention is to provide a kind of through improving the thick and large section strand from feeding capacity; Improve the method for the loose and face crack of the generous slab of thick and large section die casting, continuous cast round billets and rectangular bloom central pipe; The strand center mass is poor in the solution prior art; The surface cracks, the problem that percent defective is high.Thereby, helping developing the round base of diameter greater than 500mm, thickness is greater than square billet or the rectangular bloom manufacturing technology of 400mm.
Based on this purpose, technical scheme of the present invention is:
A kind of method that improves the thick and large section strand from feeding capacity behind pouring metal melt, is forced cooling through modes such as mould water-cooled, direct water spray, spraying or blowings to the strand outer surface immediately, makes strand outer surface rapid solidification crust; Treat that the strand hull-skin temperature is reduced to 800~1000 ℃, when solidified layer thickness reaches the 5-30% of casting blank section thickness or diameter, stop outer surface and force cooling.
Described raising thick and large section strand, stops external strand outer surface and forces cooling when solidified layer thickness reaches 50-300mm from the method for feeding capacity.
Described raising thick and large section strand is controlled strand outer surface cooling condition from the method for feeding capacity, and the temperature maintenance that makes the strand outer surface is between 200~400 ℃ of subsolidus, and strand outer surface solidification layer is in the plastically deforming area of low resistance of deformation.
Described raising thick and large section strand is from the method for feeding capacity; The strand outer surface adopts insulation material or stay-warm case that the strand outer surface is incubated after stopping to force cooling then, reduces strand outer surface and extraneous heat transfer intensity; Utilizing the strand core to return heat raises the strand hull-skin temperature; Reduce the strand radial symmetry gradient, make the strand core get into mushy zone simultaneously, the strand core is solidified simultaneously.
Described raising thick and large section strand is from the method for feeding capacity; When core metal liquid solidifies simultaneously; Solidification shrinkage produces radially tension, and action of pulling stress is in outer surface high temperature solidification layer, and making, plastic deformation takes place in the frozen metal; To the strand center plasticity taking place by outer surface and move, realizes that strand is radially from feeding.
Described raising thick and large section strand is from the method for feeding capacity, and the strand core solidifies simultaneously, and realizes that casting billet surface and core still are in the condition of high temperature radially after feeding; Carry out high temperature this moment and mould adobe blocks, the strand calcining temperature is greater than 800 ℃.
Described raising thick and large section strand is from the method for feeding capacity, and the strand calcining temperature is preferably 850-1200 ℃.
Described raising thick and large section strand is from the method for feeding capacity, and this method is applicable to continuous casting square billet or the rectangular bloom of thickness greater than 400mm, diameter greater than the continuous cast round billets of 500mm and thickness greater than the generous slab of the die casting of 600mm.
The invention has the beneficial effects as follows:
1, on the traditional sense, feeding a casting is many carries out the axis feeding along gravity direction, and the present invention is through control strand external refrigeration condition, realized in the casting blank solidification process perpendicular to gravity direction radially from feeding.
2, the present invention is at the thick and large section casting blank solidification initial stage; Adopt water-cooled, the cold or air-cooled mode of mist to improve strand and outside interface heat exchange coefficient; Casting billet surface is solidified rapidly; Set up casting billet surface intensity fast, prevent that early solidification casting billet surface solidified layer thickness is thinner, intensity is crossed low and fire check that produce.
3, among the present invention; During the 5-30% of casting blank solidification layer thickness cross section diameter or thickness (being generally 50-300mm); Stop the outside pressure cooling of strand, the outer regional temperature that solidified this moment is lower, is used to the strand core and does not solidify the zone low temperature external environment condition is provided; Guarantee the setting rate of core metal liquid, avoid core crystal grain too thick.
4, the present invention was incubated casting billet surface in the casting blank solidification middle and later periods, made casting billet surface be warming up to the plastic zone, helped preventing that casting billet surface receives big thermal stress and cracks.
5, the present invention was incubated casting billet surface in the casting blank solidification middle and later periods; Can reduce thick and large section strand thermograde from inside to outside; Make strand center large area region get into mushy zone simultaneously, solidify simultaneously at realization strand center, avoids concentrating the generation of shrinkage cavity defect.
6, adopt the method that the present invention relates to; When strand center large tracts of land is solidified simultaneously; Because solidification shrinkage produces radially tension; Order about the high temperature solid-state metal that solidified the strand outside and take place to move by the plasticity of casting billet surface to the center, realize the casting blank solidification process radially from feeding, improve even eliminate strand internal shrinkage rarefaction defect.
7, adopt the method that the present invention relates to, give full play to the thick and large section strand, can reduce strand rising head size, further improve the stock utilization of thick and large section strand radially from feeding capacity.
8, the scope of application of the present invention is wider, can be used for producing thick and large section continuous cast round billets, square billet or rectangular bloom, also can be used for the generous slab of production die casting, also can be used for producing other thick and large section casting parts.
9, adopt the method that the present invention relates to that the demoulding of strand realization high temperature, heat are sent, enhance productivity energy efficient.
In a word, the present invention at first makes the strand outer surface solidify crust rapidly through the external refrigeration condition of the different solidification stages of control strand, sets up intensity, prevents face crack; Then casting billet surface is incubated slow cooling, makes the core large tracts of land be in mushy zone, strand outer surface solidification layer maintains higher temperature to help realizing plastic deformation; And then solidify and solid phase movement when realizing in the follow-up solidification shrinkage process of strand, the deformable metal that reaches a high temperature is radially from the purpose of feeding, thereby eliminates strand internal shrinkage and face crack, and significantly improves until eliminating strand inner loose.Simultaneously, this method can realize that the strand elevated temperature heat send, and enhances productivity, and realizes purpose of energy saving.The present invention is applicable to thick and large section metal strand, and it is big to be particularly useful for ratio of height to diameter, can't improve axis loose thick and large section continuous cast round billets and square billet through riser feeding.
Description of drawings
The generous slab of the water-cooled die casting that Fig. 1 adopts the present invention to produce.
The thick and large section continuous cast round billets that Fig. 2 adopts the present invention to produce.Wherein, Fig. 2 (a) is a thick and large section continuous cast round billets pictorial diagram, and Fig. 2 (b) is the continuous cast round billets cross section.
The center that Fig. 3 does not adopt the present invention to produce has the continuous cast round billets of shrinkage cavity defect.Wherein, Fig. 3 (a) is a thick and large section continuous cast round billets pictorial diagram, and Fig. 3 (b) is the continuous cast round billets cross section.
The specific embodiment
The present invention eliminates internal shrinkage and face crack, improves loose method through improving the thick and large section strand from feeding capacity, and implementation step and mode are following:
1, adopts smelting equipments such as electric induction furnace or electric arc furnaces to carry out the molten steel melting, carry out the deoxidation degasification then.
2, the pouring molten steel of melting being handled well is in generous slab die cavity of die casting or continuous casting crystallining.
3, through water-cooled mould, crystallizer the strand outer surface is forced cooling, make the strand outer surface solidify crust rapidly, also can adopt water spray, spraying or air blowing mode, strengthen the external heat exchange of strand.
4, force to adopt contact or contactless temperature-measuring monitoring of equipment casting blank surface temperature in the cooling procedure at casting billet surface, control casting blank surface temperature as far as possible at 800~1000 ℃.Prevent that temperature is low excessively, solid-state phase changes generation structural stress takes place and brings out crackle in the frozen metal; Avoid temperature too high equally, solidified layer thickness is thin, intensity is lower, and " bulge " takes place casting billet surface under the molten metal static pressure, forms crackle.
5, treat that the casting blank solidification layer thickness reaches 50-300mm after, stop casting billet surface being forced cooling, then casting billet surface is incubated.Casting blank surface temperature constantly rises, monitoring strand hull-skin temperature, and regulate strand and outside interfacial heat exchange intensity, make casting blank surface temperature maintain the plastically deforming area of 200~400 ℃ of material subsolidus.
6, the thermograde of strand center and outer surface reduces gradually, and strand central area large tracts of land gets into mushy zone.In follow-up cooling procedure, the strand center realizes solidifying simultaneously; Solidification shrinkage produces tension, and the solid metallic generation plastic deformation that impels the strand outer surface to solidify is moved to center plasticity by casting billet surface, realize the casting blank solidification process radially from feeding.
Embodiment 1
This embodiment adopts the generous slab of method production die casting that the present invention relates to, and generous slab material is Q345, and generous slab thickness is 1000mm, and gross mass is 60 tons.
Adopt electric arc furnaces to carry out the molten steel melting, again through the refining of LF stove, change molten steel over to the VD stove then and carry out the deoxidation degasification, molten steel is poured in the time of 1560 ℃ in the split type water-cooled mould, and be 30min total duration of pouring.Learn that through computer Simulation cast finishes back 40min, generous slab surface solidification layer thickness is 90mm.Reduce water-cooled mould discharge this moment, and increase the gap between mould and the generous slab, reduce generous slab surface radiating speed.Monitor generous slab surface temperature and change discovery, generous slab surface temperature is increased to 1100 ℃~1250 ℃ by 920 ℃, and the strand temperature slowly descends afterwards, until solidifying fully.
The generous slab that Fig. 1 produces for present embodiment, nondestructive inspection are found, the loose shrinkage cavity defect of the inner nothing of continuous casting steel ingot, and cc billet surface quality is intact, does not find face crack.
Embodiment 2
This embodiment adopts the method that the present invention relates to produce the thick and large section continuous cast round billets, and circle base material is 20CrNi2Mo, and diameter is 1000mm, and length is 8m, and circle base gross weight is 45 tons.
The pouring molten steel that melting is handled well is in crystallizer, and pouring temperature is 1540 ℃, and the strand casting speed is 0.1m/min.Through analog computation, when strand was drawn out crystallizer, the surface solidification layer thickness was about 50mm, and surface temperature is about 850 ℃.Strand promptly adopts insulation material that casting billet surface is incubated once pulling out crystallizer, and casting blank surface temperature is increased to 1200~1260 ℃, is in the plastic zone.Strand thermograde from inside to outside is less, has realized that the central area solidifies simultaneously.In the subsequent cooling process, strand outer surface generation plastic deformation, the solid phase ecto-entad shrinks mobile, has realized radially feeding.
Shown in Fig. 2 (a), adopt the thick and large section continuous cast round billets of the technology production that the present invention relates to for present embodiment.Find through nondestructive inspection, the inner no shrinkage cavity defect of strand, casting billet surface is the flawless defective also.Be depicted as round base cross section like Fig. 2 (b), the center does not have concentrated shrinkage cavity defect, and loose rank is less than 2 grades.
Shown in Fig. 3 (a), embodiment of the present invention does not relate to the continuous cast round billets of technological comparable size specification of being produced.Circle base center exists large tracts of land shrinkage cavity and rarefaction defect, shown in Fig. 3 (b).
The result shows; The present invention makes strand center large tracts of land get into mushy zone through the external refrigeration condition of the different solidification stages of control strand, makes strand outer surface solidification layer maintain higher temperature simultaneously; Realized that the solid phase plasticity in the follow-up solidification shrinkage process of strand moves; Reached the high temperature deformable metal radially from the purpose of feeding, it is loose to have improved the strand internal shrinkage, and has prevented the generation of external crack.